1. Field of the Invention
The present invention relates to anti-backlash damping of gears and more particularly to third order damping which removes backlash and improves gear life by reducing pre-load forces and eliminating backlash crossover.
2. Description of the Prior Art
Backlash, i.e., the gap between teeth of mating gears, is inherent to most gear transmission designs. It is undesirable because it causes a dead-band which produces a loss of precision in output position and velocity control. Apparatus for reducing backlash is known in the prior art and normally takes the form of a second, or anti-backlash gear adjacent the driving gear which is substantially identical to the driving gear but is off-set there from, under the force of a pre-load mechanism such as a spring so that the combined backlash gear and driving gear fill the space between the surfaces of the driven gear teeth.
Unfortunately, the pre-load force tends to reduce gear life by causing excess wear and material fatigue. Typically, the higher the pre-load, the shorter the gear life. Also, in cases where high control bandwidth is necessary, the pre-load force is not sufficient to filly eliminate backlash xe2x80x9ccrossoverxe2x80x9d i.e. the travel of the driving gear from one flank of the driven gear to the other flank across the backlash gap. This limits the bandwidth and results in significant transmission error.
The present invention overcomes the problems with anti-backlash arrangements of the prior art by using a third order damper in place of the pre-load force. Third order dampers have been described in paper by Porter Davis, David Cunningham and John Harrell presented at the 35th AIAA SDM Conference, April 1994. It may also be seen in U.S. Pat. No. 5,332,070 of Lawrence P. Davis, et al., entitled xe2x80x9cThree Parameter Viscous Damper and Isolatorxe2x80x9d which issued Jul. 26, 1994 with serial number 51,110 and is assigned to the assignee of the present invention. Applying a third order damper to an anti-backlash gear arrangement, improves the bandwidth capability, mitigates the transmission errors, and reduces the pre-load forces to increase gear life in the anti-backlash gears of the prior art.